Polypropylenes which are reinforced with a glass fiber are excellent in chemical resistance, and they are also excellent in strength as compared with other polypropylenes which are reinforced with a lamellar filler or a granular filler. Furthermore, they are inexpensive, and so they are now used as useful industrial materials in many fields.
However, the glass fiber-reinforced polypropylenes are crystalline resins, and therefore they have the drawback that the warpage of molded articles thereof is larger as compared with glass fiber-reinforced articles of non-crystalline resins. Accordingly, as a means for inhibiting the warpage deformation, a technique is disclosed in which a rubber component such as an elastomer is added, but when the rubber component is added, strength and stiffness noticeably deteriorate.
Furthermore, techniques in which the glass fiber and the mica powder of the lamellar filler are used together are disclosed in Japanese Patent Application Laid-open Nos. 58-206659 and 61-98758, and it is described in these publications that materials having high strength and stiffness and excellent dimensional accuracy can be obtained.
On the other hand, techniques in which a small amount of the glass fiber is blended for the purpose of improving the strength of the polypropylene filled with the mica powder are disclosed in Japanese Patent Application Laid-open Nos. 52-36141, 55-45715, 55-40719 and 60-23432.
In techniques in which the polypropylenes are compositely reinforced with the glass fiber and the mica powder, the interface adhesion between the filler and the matrix resin has been investigated to improve strength by a process of grafting an unsaturated silane on the matrix resin, a process of grafting an unsaturated acid or a process of blending an isocyanate compound and an epoxy compound with the matrix resin.
In all of these techniques, however, only initial strength has been inspected, and with regard to mechanical durability in the case that load is applied for a long period of time or applied repeatedly, no inspection has been made at all.
On the other hand, Japanese Patent Application Laid-open No. 60-1235 discloses that in the blend system singly containing the glass fiber, a resin composition is used which can be obtained by melting and kneading an unsaturated acid and an unsaturated silane simultaneously with a polypropylene in the presence of an organic peroxide.
However, this technique also intends to improve the initial strength as in the above-mentioned cases, and the mechanical durability has not been inspected at all.
As discussed above, the polypropylenes which are compositely reinforced with glass fibers and mica powder can provide molded articles having high strength and stiffness, less warpage deformation and excellent dimensional accuracy, and therefore they are industrially useful materials. However, under conditions where load is continuously applied for a long period of time or that load is applied repeatedly, durability is often insufficient, and the utilization of these polypropylenes has been restricted in many cases.
An object of the present invention is to provide a polypropylene resin composition which permits the formation of materials having high strength and stiffness, less warpage deformation and such excellent mechanical durability that these materials can be used when a load is applied continuously for a long term or when a load is applied repeatedly.